The present invention relates to processes for petroleum refining and, more specifically, to processes for petroleum refining to obtain petroleum products having a reduced content of sulphur, oxygen- and nitrogen-containing compounds.
Petroleum and primary refinery products such as gasoline and kerosene are extensively used as fuel components for internal combustion engines, as well as for jet and diesel fuels, fuel oils and starting stock for catalytical cracking.
Gasoline, kerosene, and diesel fuel produced from high-sulphur-content crudes and medium-sulphur content crudes contain total and mercaptan sulphur. For example, mercaptan content in kerosene may be as high as 0.008% by weight although the tolerable content is at most 0.005% by weight. The increased content of sulphur and sulphur compounds substantially impairs the service properties of petroleum products, resulting in reduced motor service life due to accelerated wear of vital parts and decreasing the economic efficiency thereof. In addition, increased sulfur content contributes to increased air pollution by producing acidic combustion products.
Reactive nitrogen- and oxygen-containing resin-forming compounds as well as naphthenic acids cause a reduced fuel stability upon storage due to formation of gums.
Various processes, for the removal of sulphur and sulphur compounds, contemplating treatment of products resulting from petroleum refining such as by treatment with sulphuric acid, adsorbents, hydrofining and the like are known in the art. In those prior art processes, as a rule, petroleum is first subjected to distillation, and thereafter each individual fraction is treated. However, from an economic point of view it is preferred to perform distillation and purification in one technological step.
A known process for desulfurization of hydrocarbons (U.S. Pat. No. 2,306,933) involves removing hydrogen sulphide, heating the petroleum separating the light and heavy fraction, treating the heavy fractions using conditions which facilitate formation of mercaptans at temperatures up to 204.4.degree. C. (400.degree. F.) by means of a reagent to convert non-mercaptan sulphur to mercaptans. This treatment is followed by reacting the heavy fraction with a metal carbonyl at a temperature of from 148.9.degree. to 343.degree. C. (300.degree. to 650.degree. F.) and separating any unreacted metal carbonyl.
Also known in the art is a process for purifying products resulting from petroleum refining to remove sulphur, sulphur compounds, reactive nitrogen- and oxygen-containing compounds and naphthenic acids (Belgian Patent No. 809,377) which process comprises purifying petroleum or its primary refinary products with compounds of transition metals at a temperature of from 80.degree. to 120.degree. C. Suitable transition metal compounds include volatile carbonyl compounds of transition metals, .pi.-complexes of transition metals, salts or .pi.-allyl complexes of metals of the platinum group, and carbonyl complexes of transition metals. As a result, a reaction mixture is obtained from which the desired purified product is isolated. This process is also applicable to the refining of crude petroleum. However, when used to refine crude petroleum, the process is practiced in two stages: purification treatment of crude petroleum and its subsequent distillation. Although this process is one of the most efficient known, it has some disadvantages. Its principal disadvantage resides in its use of volatile reagents for the purification which may accumulate in the final products, thus requiring the use of additional chelating agents to eliminate said reagents from the final products. All the above-described processes are applicable only to purification treatment of petroleum fractions, i.e. to products of petroleum refining, not to purification of crude petroleum and, therefore are incompatible with petroleum distillation.